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Biomedical subjects

Moo-Song Lee

Publications and source records attributed to Moo-Song Lee.

At least 19 recordsLinked to original sources

Determinants of hospital closure in South Korea: use of a hierarchical generalized linear model.

Understanding causes of hospital closure is important if hospitals are to survive and continue to fulfill their missions as the center for health care in their neighborhoods. Knowing which hospitals are most susceptible to closure can be of great use for hospital administrators and others interested in hospital performance. Although prior studies have identified a range of factors associated with increased risk of hospital closure, most are US-based and do not directly relate to health care systems in other countries. We examined determinants of hospital closure in a nationally representative sample: 805 hospitals established in South Korea before 1996 were examined-hospitals established in 1996 or after were excluded. Major organizational changes (survival vs. closure) were followed for all South Korean hospitals from 1996 through 2002. With the use of a hierarchical generalized linear model, a frailty model was used to control correlation among repeated measurements for risk factors for hospital closure. Results showed that ownership and hospital size were significantly associated with hospital closure. Urban hospitals were less likely to close than rural hospitals. However, the urban location of a hospital was not associated with hospital closure after adjustment for the proportion of elderly. Two measures for hospital competition (competitive beds and 1-Hirshman--Herfindalh index) were positively associated with risk of hospital closure before and after adjustment for confounders. In addition, annual 10% change in competitive beds was significantly predictive of hospital closure. In conclusion, yearly trends in hospital competition as well as the level of hospital competition each year affected hospital survival. Future studies need to examine the contribution of internal factors such as management strategies and financial status to hospital closure in South Korea.

Economics, Hospital↗

Quantitative analysis of viral RNA in the murine heart and pancreas with different concentration of coxsackievirus B3.

OBJECTIVES: We investigated the clinical features, pathologic changes, and viral RNA kinetics in the course of acute and subacute experimental coxsackievirus B3 (CVB3) infection in a murine model. METHODS: Five-week-old A/J inbred male mice were divided into 5 groups. Four of those groups were inoculated intraperitoneally with 5 x 10(4) (group 1), 1 x 10(5) (group 2), 5 x 10(5) (group 3), or 1 x 10(6) (group 4) PFU of CVB3. Control mice were inoculated with uninfected Vero cell lysate in DMEM. Mice from each group were sacrificed on days 7 or 14 after inoculation. RESULTS: Bloody diarrhea, earlier weight loss, perianal swelling, and death were correlated with higher viral load. One of ten mice in group 3 and 5 of 10 mice in group 4 died spontaneously between days 4 and 12 after inoculation. All of the remaining 34 mice of infected groups demonstrated extensive pancreatic inflammation. Focal myocarditis developed in only 4 (11.8%) of those 34 subjects. Amylase and creatine kinase activities in the serum were increased in the mice of infected groups. CVB3 RNA was detected in the heart and pancreatic tissue in all subjects. The CVB3 RNA copy number in pancreatic tissue was not correlated with the severity of inflammation. CONCLUSIONS: In the murine model, viral loading dose determines the clinical features of CVB3-induced infection, and the severity of pancreatitis is not correlated with the viral loading dose or tissue level of viral RNA. .

Amylases↗

High body mass index and dietary pattern are associated with childhood asthma.

The increasing prevalence of asthma has coincided with an increase of body mass index (BMI) in both children and adults. We investigated the relationship between BMI and the symptom prevalence of asthma and the possible influences of dietary pattern. This was a community-based, cross-sectional study of 24,260 school children aged 6-12 years. Prevalences of asthma and potential confounding factors were assessed using a Korean version of the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire which was completed by parents. We analyzed the relationship between BMI and symptoms of asthma and the possible influences of dietary pattern. A significant positive association between high BMI and previous 12-month prevalence of wheeze remained in boys (adjusted odds ratio, 1.610; 95% confidence interval, 1.274-2.033) but not in girls. In addition, there were significant associations between high BMI and lifetime prevalence of wheeze, previous 12-month wheeze, exercise-induced wheeze, diagnosis, and treatment of asthma. There were significant associations between high BMI and previous 12-month wheeze regardless of breast-milk feeding or whole-milk feeding. Frequent intake of fresh seafood, fresh fruits, and vegetables was associated with reduced prevalence of current asthma symptoms and was also associated with decreased BMI. These results indicate that BMI may be an independent risk factor for the development of asthma symptoms in boys. Intake of fresh seafood, fresh fruit, and vegetables, which may be associated with decreased BMI, may contribute to protect against the development of asthma symptoms in Korean elementary schoolchildren.

Asthma↗

Prostate cancer in Korean men exhibits poor differentiation and is adversely related to prognosis after radical prostatectomy.

OBJECTIVES: To investigate the clinical and pathologic characteristics of prostate cancer in Korean men to determine how ethnic differences affect clinical outcome. METHODS: The clinical and pathologic data of 604 Korean men who underwent radical prostatectomy from 1994 to 2003 were reviewed. Biochemical failure was defined as a prostate-specific antigen (PSA) level of 0.2 ng/mL or greater on two consecutive occasions after having achieved an undetectable PSA level. Patient distribution with respect to the clinical and pathologic parameters and biochemical failure rates were compared with those of contemporary Western series. RESULTS: The mean preoperative PSA level was 9.9 ng/mL (range 0.4 to 38.8) and the median biopsy Gleason score was 7. The Gleason score was 7 in 186 patients (30.8%) and greater than 7 in 169 (28.0%). Gleason scores stratified with respect to clinical stage and PSA range revealed the proportion of patients with high Gleason scores (7 or greater) to be more than 50% of each subgroup throughout the clinical stages and PSA ranges. At a median follow-up of 57.9 months (range 22 to 131), biochemical failure occurred in 24.2% of all patients and in 14.3% of those with an initial serum PSA level of 10.0 ng/mL or lower. On multivariate Cox regression analysis, the Gleason score showed the strongest statistical significance for biochemical failure (P = 0.001, hazard ratio 1.376, 95% confidence interval 1.056 to 1.792) for patients with a serum PSA level of 10.0 ng/mL or lower. CONCLUSIONS: A significant proportion of prostate cancers arising in Korean men exhibit poor differentiation, regardless of the initial serum PSA level or clinical stage at presentation, and adversely affect prognosis, causing a greater rate of PSA failure.

Adult↗

Comparison of mangafodipir trisodium- and ferucarbotran-enhanced MRI for detection and characterization of hepatic metastases in colorectal cancer patients.

OBJECTIVE: The purpose of our study was to evaluate the validity of mangafodipir trisodium-enhanced versus ferucarbotran-enhanced MRI in the detection and characterization of hepatic lesions in colorectal cancer patients. MATERIALS AND METHODS: Forty-one patients who were known to have or suspected of having hepatic metastasis from colorectal carcinoma underwent mangafodipir trisodium- or ferucarbotran-enhanced MRI in block randomization methods. Two radiologists independently reviewed the MR images to determine the number of hepatic lesions and to characterize the lesions as malignant or benign. Each lesion was assessed according to its size (small, 2 cm in diameter) on both mangafodipir trisodium- or ferucarbotran-enhanced MRI. The data were correlated with the reference diagnosis: histopathology and intraoperative sonography (n = 16); intraoperative sonography (n = 4); and imaging and clinical diagnosis with follow-up (> 3 months; n = 21). The detection rates and diagnostic accuracies of hepatic lesions on both sets of MR images were assessed using Fisher's exact test. RESULTS: Eighty-two hepatic lesions (53 metastatic and 29 benign) were identified in 41 patients. No significant differences were seen between mangafodipir trisodium- and ferucarbotran-enhanced MRI for detecting all hepatic lesions (p = 0.183), small hepatic lesions (p = 0.299), all metastases (p = 0.695), and small metastases (p = 0.689). The diagnostic accuracies of mangafodipir trisodium- and ferucarbotran-enhanced MRI showed no significant differences in all hepatic lesions (p = 0.624) and small hepatic lesions (p = 0.641). CONCLUSION: Mangafodipir trisodium- and ferucarbotran-enhanced MRI are similar in hepatic lesion detection and characterization in colorectal cancer patients.

Adult↗

Association of the GSTP1 and NQO1 polymorphisms and head and neck squamous cell carcinoma risk.

The GSTP1 and NQO1 have been reported to be associated with an increased risk for smoking related head and neck squamous cell carcinoma (HNSCC). The purpose of this study was to determine the effect of these metabolic gene polymorphisms on the risk of HNSCC. The study population included 294 histologically confirmed HNSCC cases and 333 controls without cancer. Genotyping analysis of the GSTP1 Ile105Val and NQO1 Trp139Arg genes was performed by polymerase chain reaction-based techniques on DNA prepared from peripheral blood. The Mantel-Haenszel chi2 test was used for statistical analysis. The allele frequencies of the GSTP1 and NQO1 polymorphisms were not statistically significant between cases and controls. In analyzing the association between smoking amounts and genetic polymorphisms, GSTP1 and NQO1 polymorphisms were associated with cigarette smoking amounts in cases. G allele containing genotypes in GSTP1 and T allele containing genotypes in NQO1 were associated with a tobacco dose-dependent increase in risk of HNSCC and these genotype distributions were statistically significant (p<0.05). We found that the GSTP1 105Val allele and NQO1 139Arg allele were associated with tobacco dose-dependent increase in risk of HNSCC. GSTP1 and NQO1 genotype polymorphisms may play an important role in the development of smoking related HNSCC.

Adult↗

HGLM versus conditional estimators for the analysis of clustered binary data.

Clustered binary data arise frequently in medical research such as cross-over clinical trials and twin studies. For the analysis of such data either a random-effects model or a conditional likelihood approach can be used. In this paper, we compare numerically the random-effects model estimator and the conditional likelihood estimator and discuss their relative merits for the analysis of binary data.

Age Factors↗

Effect modification by vitamin C on the relation between gastric cancer and Helicobacter pylori.

A hospital-based case-control study of 295 cases with histologically confirmed gastric cancer and age and sex-matched controls was conducted to evaluate the effect of dietary vitamin C intake upon the relation between Helicobacter pylori infection and gastric cancer in Korea in 1997-1998. Anti-H. pylori IgG was detected by ELISA. A food frequency questionnaire, and a questionnaire on demographic factors, including past medical history, smoking, alcohol consumption, and life style was also administered. The prevalences of H. pylori IgG in cases and controls were 80.7% and 71.2%, respectively, and the odds ratio (OR) of H. pylori for gastric cancer was 1.68 (95% confidence interval (CI): 1.14, 2.44), after adjusting for age, sex, educational level, and a past medical history of gastritis or gastric ulcer. In a stratified analysis, H. pylori seropositivity was found to be a significant risk factor for gastric cancer in the low vitamin C intake group (OR = 4.68; 95% CI: 1.97, 11.1), but not in the high vitamin C intake group (OR = 0.72; 95% CI: 0.32, 1.65). Vitamin C intake was found to modify the relation between H. pylori and gastric cancer.

Adult↗

Fever, use of antibiotics, and acute gastroenteritis during infancy as risk factors for the development of asthma in Korean school-age children.

OBJECTIVE: The hygiene hypothesis postulates that infections early in life might influence the development of asthma later in childhood. However, this hypothesis is controversial. The objective of this study was to determine whether there is a relationship between infection-related risk factors during infancy and development of asthma later in childhood. METHODS: Data were obtained by a nationwide, population-based, cross-sectional study of 26,400 children, 7 to 12 years of age. Parents completed a questionnaire on symptoms of and risk factors for asthma, including the number of fever episodes, acute gastroenteritis, use of antibiotics, and immunization during infancy. The presence of asthma was defined by parental report of "wheeze in the last 12 months" or "asthma ever." Data were analyzed by logistic regression analysis. RESULTS: The occurrence of fever during infancy was weakly associated with the development of asthma (P < 0.05). A higher frequency of episodes of fever was associated with a higher risk of development of asthma. The relationship between antibiotic use during infancy and development of asthma was also significant (P < 0.0001). The adjusted odds ratios of childhood asthma increased in proportion to the number of antibiotic courses during infancy. A history of acute gastroenteritis during infancy increased the risk of developing asthma in later life (P < 0.001). In contrast, immunization in infancy was not related to development of asthma in childhood (P > 0.05). CONCLUSIONS: These data suggest that the development of childhood asthma is associated with episodes of fever, antibiotic use, and acute gastroenteritis during infancy.

Age Factors↗

Korean red ginseng slows depletion of CD4 T cells in human immunodeficiency virus type 1-infected patients.

We have previously showed that long-term intake of Korean red ginseng (KRG) delayed disease progression in human immunodeficiency virus type 1 (HIV-1)-infected patients. In the present study, to investigate whether this slow progression was affected by KRG intake alone or in combination with HLA factor, we analyzed clinical data in 68 HIV-1-infected patients who lived for more than 5 years without antiretroviral therapy. The average KRG intake over 111.9 +/- 31.3 months was 4,082 +/- 3,928 g, and annual decrease in CD4 T cells was 35.0 +/- 28.7/microl. Data analysis showed that there are significant inverse correlations between the HLA prognostic score (0.29 +/- 1.19) and annual decrease in CD4 T cells (r = -0.347; P < 0.01) as well as between the amount of KRG intake and annual decrease in CD4 T cells (r = -0.379; P < 0.01). In addition, KRG intake significantly slowed the decrease in CD4 T cells even when influence of HLA class I was statistically eliminated (repeated-measure analysis of variance; P < 0.05). We also observed significant correlation between KRG intake and a decrease in serum-soluble CD8 antigen level (r = 0.62; P < 0.001). In conclusion, these data show that KRG intake independently and significantly affected the slow depletion of CD4 T cells irrespective of HLA class I.

CD4 Lymphocyte Count↗

Nomograms for the prediction of pathologic stage of clinically localized prostate cancer in Korean men.

We analyzed the prostate cancer data of 317 Korean men with clinically localized prostate cancer who underwent radical prostatectomy at Asan Medical Center between June 1990 and November 2003 to construct nomograms predicting the pathologic stage of these tumors, and compared the outcome with preexisting nomograms. Multinomial log-linear regression was performed for the simultaneous prediction of organ-confined disease (OCD), extracapsular extension (ECE), seminal vesicle invasion (SVI) and lymph node metastasis (LNM) using serum prostate-specific antigen (PSA), Gleason score and clinical stage. Nomograms representing percent probabilities were constructed and compared with those presented by Partin et al. by calculating areas under the receiver operating characteristics (ROC) curves. Median serum PSA at surgery was 10.8 ng/mL, and median biopsy Gleason score was 7. Overall OCD, ECE, SVI and LNM rates were 59.6%, 20.5%, 11.7% and 8.2%, respectively, and areas under the curves were 0.724, 0.626, 0.662, and 0.794, respectively. Pathologic stage of localized prostate cancer in Korean men may be predicted using the Partin table, with acceptable accuracy for OCD and LNM, but less so for ECE and SVI.

Adult↗

Anti-leukemic effect of graft-versus-host disease on bone marrow and extramedullary relapses in acute leukemia.

BACKGROUND AND OBJECTIVES: Several reports have suggested that the graft-versus-leukemia effect at extramedullary (EM) sites might be less prominent than that in the bone marrow (BM). We analyzed the effect of graft-versus-host disease (GVHD) on BM and EM relapses in 194 consecutive patients with acute leukemia who underwent allogeneic hematopoietic cell transplantation at a single institute. DESIGN AND METHODS: We compared relapse-free survival (RFS), BM RFS, and EM RFS after allografting according to the occurrence of GVHD. We also investigated the clinical outcome of patients who relapsed after their allogeneic transplantation. RESULTS: Relapse occurred in 65 patients; in 41 (63%) relapse occurred in the BM only, in 9 (14%) it occurred in both BM and EM sites, and 15 (23%) in EM sites only. Patients who developed acute GVHD after transplantation had significantly higher relapse-free survival (69.2% vs. 52.4%; p=0.042) and BM RFS (80.7% vs. 59.1%; p=0.030) compared to those who did not. However, EM RFS was similar between patients with and without acute GVHD (76.7% vs. 78.2%; p=0.744). Among the 65 patients who relapsed, 32 patients attained complete remission with salvage treatments and 22 experienced a second relapse, which occurred in the BM (n=9), BM and EM sites (n=1), or EM sites (n=12). INTERPRETATION AND CONCLUSIONS: Our study confirms that GVHD after allogeneic hematopoietic cell transplantation has an anti-leukemic effect, thus preventing relapse; however, it may be less effective in preventing EM relapse.

Adolescent↗

[Census population vs. registration population: which population denominator should be used to calculate geographical mortality].

OBJECTIVES: Studies on the geographical differences in mortality tend to use a census population, rather than a registration population, as the denominator of mortality rates in South Korea. However, an administratively determined registration population would be the logical denominator, as the geographical areas for death certificates (numerator) have been determined by the administratively registered residence of the deceased, rather than the actual residence at the time of death. The purpose of this study was to examine the differences in the total number of a district population, and the associated district-specific mortality indicators, when two different measures as a population denominator (census and registration) were used. METHODS: Population denominators were obtained from census and registration population data, and the numbers of deaths (numerators) were calculated from raw death certificate data. Sex- and 5-year age-specific numbers for the populations and deaths were used to compute sex- and age-standardized mortality rates (by direct standardization methods) and standardized mortality ratios (by indirect standardization methods). Bland-Altman tests were used to compare district populations and district-specific mortality indicators according to the two different population denominators. RESULTS: In 1995, 9 of 232 (3.9%) districts were not included in the 95% confidence interval (CI) of the population differences. A total of 8 (3.4%) among 234 districts had large differences between their census and registration populations in 2000, which exceeded the 95% CI of the population differences. Most districts (13 of 17) exceeding the 95% CI were rural. The results of the sex- and age-standardized mortality rates showed 15 (6.5%) and 16 (6.8%) districts in 1995 and 2000, respectively, were not included in the 95% CI of the differences in their rates. In addition, the differences in the standardized mortality ratios using the two different population denominators were significantly greater among 14 districts in 1995 and 11 districts in 2002 than the 95% CI. Geographical variations in the mortality indicators, using a registration population, were greater than when using a census population. CONCLUSION: The use of census population denominators may provide biased geographical mortality indicators. The geographical mortality rates when using registration population denominators are logical, but do not necessarily represent the exact mortality rate of a certain district. The removal of districts with large differences between their census and registration populations or associated mortality indicators should be considered to monitor geographical mortality rates in South Korea.

Censuses↗

[Changes in mortality inequality in relation to the South Korean economic crisis: use of area-based socioeconomic position].

OBJECTIVES: An abrupt economic decline may widen the socioeconomic differences in health between the advantaged and disadvantaged in a society. The aim of this study was to examine whether the South Korean economic crisis of 1997-98 affected the socioeconomic inequality from all-causes and from cause-specific mortality between 1995 and 2001. METHODS: Population denominators were obtained from the registration population data, with the number of death (numerators) calculated from raw death certificate data. The indicator used to assess the geographic socioeconomic position was the per capita regional tax revenue. Administrative districts (Si-Gun-Gu) were ranked according to this socioeconomic measure, and divided into equal population size quintiles on the basis of this ranking. The sex- and 5-year age-specific numbers of the population and deaths were used to compute the sex- and age-adjusted mortality rates (via direct standardization method), standardized mortality ratios (via indirect standardization methods) and relative indices of inequality (RII) (via Poisson regression). RESULTS: Geographic inequalities from all-causes of mortality, as measured by RII, did not increase as a result of the economic crisis (from 1998-2001). This was true for both sexes and all age groups. However, the cause-specific analyses showed that socioeconomic inequalities in mortalities from external causes were affected by South Korean economic crisis. For males, the RIIs for mortalities from transport accidents and intentional self-harm increased between, 1995 and 2001. For females, the RII for mortality from intentional self-harm increased during the same period. CONCLUSIONS: The South Korean economic crisis widened the geographic inequality in mortalities from major external causes. This increased inequality requires social discourse and counter policies with respect to the rising health inequalities in the South Korean society.

Adolescent↗

[Socioeconomic differentials in health and health related behaviors: findings from the Korea Youth Panel Survey].

OBJECTIVE: This study examined the socioeconomic differentials for the health and health related behaviors among South Korean middle school students. METHODS: A nationwide cross-sectional interview survey of 3,449 middle school second-grade students and their parents was conducted using a stratified multi-stage cluster sampling method. The response rate was 93.3%. The socioeconomic position indicators were based on self-reported information from the students and their parents: parental education, father's occupational class, monthly family income, out-of-pocket expenditure for education, housing ownership, educational expectations, educational performance and the perceived economic hardships. The outcome variables that were measured were also based on the self-reported information from the students. The health measures included self-rated health conditions, psychological or mental problems, the feelings of loneliness at school, the overall satisfaction of life and the perceived level of stress. The health related behaviors included were smoking, alcohol drinking, sexual intercourse, violence, bullying and verbal and physical abuse by parents. RESULTS: Socioeconomic differences for the health and health related behaviors were found among the eighth grade boys and girls of South Korea. However, the pattern varied with gender, the socioeconomic position indicators and the outcome measures. The prevalence rates of the overall dissatisfaction with life for both genders differed according to most of the eight socioeconomic position indicators. All the health measures were significantly different according to the perceived economic hardship. However, the socioeconomic differences in the self-rated health conditions and the psychosocial or mental problems were not clear. The students having higher socioeconomic position tended to be a perpetrator of bullying while those students with lower socioeconomic position were more likely to be a victim. CONCLUSIONS: The perceived economic hardships predicted the health status among the eighth graders of South Korea. The overall satisfaction of life was associated with the socioeconomic position indicators. Further research efforts are needed to explore the mechanisms on how and why the socioeconomic position affects the health and health related behaviors in this age group.

Adolescent↗

Decreased incidence of hepatic veno-occlusive disease and fewer hemostatic derangements associated with intravenous busulfan vs oral busulfan in adults conditioned with busulfan + cyclophosphamide for allogeneic bone marrow transplantation.

We investigated the occurrence of hepatic veno-occlusive disease (VOD) after allogeneic bone marrow transplantation (BMT) in 241 adults conditioned with busulfan + cyclophosphamide at a single institute and retrospectively compared 186 patients who received oral busulfan (O-Bu group) with 55 patients who received intravenous busulfan (I-Bu group). Various hemostatic parameters were determined at baseline and on days 0, 7, 14, and 21. Hepatic VOD occurred in 41.7% of the O-Bu group and in 18.5% of the I-Bu group. Multivariate analysis revealed that the I-Bu group had significantly decreased risk of VOD compared to the O-Bu group [p=0.006, odds ratio: (OR) 0.345]. Eleven patients in the O-Bu group and none of the I-Bu group developed severe VOD. A repeated measures analysis of variance (ANOVA) with a between-subjects factor revealed significant differences in post-transplant levels of antithrombin III, tissue plasminogen activator (tPA), plasminogen activator inhibitor 1 (PAI-1), and D-dimer according to the occurrence of VOD. The level of antithrombin III was significantly lower, whereas the level of D-dimer was significantly higher, in the O-Bu group than in the I-Bu group. These findings show that, in adults conditioned with busulfan + cyclophosphamide, intravenous busulfan was associated with significantly decreased incidence of VOD and fewer hemostatic derangements after allogeneic BMT compared to oral busulfan.

Administration, Oral↗

Women's attitudes toward mode of delivery in South Korea--a society with high cesarean section rates.

BACKGROUND: In South Korea, cesarean section rates (i.e., the proportion of all live births delivered by cesarean section) approached 40 percent in 2000. The relative contribution of physicians and women to this high rate has been a source of debate. This study explored attitudes toward mode of delivery among South Korean women. METHODS: A nationwide cross-sectional telephone survey of 505 Korean women aged 20 to 49 years was conducted using a proportionate quota and systematic random sampling method. The response rate was 57.3 percent. Data were collected using a structured questionnaire consisting of 7 questions about vaginal and cesarean delivery. RESULTS: Over 95 percent of women preferred vaginal delivery during pregnancy and were willing to recommend this method to others. Of the women who delivered by cesarean section, 10.6 percent stated that they had requested a cesarean birth. Attitudes toward vaginal or cesarean delivery differed significantly according to a woman's education level. CONCLUSIONS: Most study participants showed more favorable attitudes toward vaginal delivery than cesarean delivery. This result does not support the assumption that the upsurge of cesarean section rates in South Korea is associated with women's positive attitudes toward cesarean section. The main cause of the rapid rise of cesarean section rates in South Korea during the past two decades have its origins in health care practitioners and the health care system in which they work.

Adult↗

Concordance odds ratios and approximate rate ratios in longitudinal twin studies.

Odds ratios derived from probandwise concordance rates are usually interpreted as increased risks in twins. Though the odds ratios in case-control studies have been shown to reflect rate ratios, few studies focused on such relationships in twin studies. The authors derived an approximate formula for the ratios of person-time incidence rates after the random assignment of twins into index twins and co-twins, i.e., incidence rate ratios. The resulting rate ratio was estimated as the product of the concordance odds ratio and a term that reflect the follow-up duration and the average time to occurrence of disease. Odds ratios coincide with rate ratios when the average time to occurrence of disease is half the duration of follow-up, although in studies spanning several decades these two measures might be different. The authors illustrated that when the incidence rate is not constant over the follow-up period as in longitudinal twin studies, the conventional odds ratio should not be used as an estimator of rate ratio.

Case-Control Studies↗